Open Coaxial Resonator Type Microwave Dielectrometer

PATENT No.3691812

Open Coaxial Resonator Type Microwave Dielectrometer makes accurate measurement possible using an evanescent mode of an open coaxial resonator, which acts as a measurement probe.

When a sample material is placed on the probe, the evanescent electrical field leaks from the probe tip into the sample material. This electrical field changes with the dielectric properties of the material, which in turn changes the resonant frequency and the Q-factor of the whole cavity. The dielectric properties are then calculated from the changed resonance. The highly accurate measurement algorithm to compute the complex permittivity, uses the electromagnetic-field distribution and resonant characteristics of the evanescent mode computed by the 3D EM-field simulator, "CST MICROWAVE STUDIO".

Electric field distribution near the measuring point

Coaxial resonator

The technical article regarding the measurement principle of this system was presented in the IEEE Microwave Theory and Techniques.

There are two types of components: oscillator type and network analyzer type. The oscillator includes a microwave signal generator and a detecter, and serves as a substitute network, thereby eliminating the need of a costly network analyzer. The network analyzer type should be used with a network analyzer of your own.

System Option

General

The open coaxial resonator type microwave dielectrometer is the system which measures dielectric properties at microwave frequencies. This system has 2 types, which use either a synthesized sweep oscillator (an alternative to a network analyzer) or a network analyzer.

The synthesized sweep oscillator type consists of an oscillator, which includes a microwave signal generator and a detector, a measurement probe, a customized software, and accessories. This is a low cost type because it does not have expensive measurement devices. The network analyzer type sets up with your network analyzer to use. It consists of a measurement probe, a customized software, and accessories.
(*Please see the movie titled "2.System Components" on the top page.)

The strongest point of the microwave dielectrometer is its ease of use. This system enables fast and non-destructive measurement of dielectric materials, because the probe can handle materials of any shapes as long as there is one flat surface. In addition, the microwave dielectrometer has highly accurate measurement software. By simply placing the material on the surface of the probe, and following an easy step-by-step operation of the software wizard, the measurement is achieved for complex dielectric properties very accurately and very simply.
(*Please see the movies titled "1.AET Microwave Dielectrometer" and "4.Actual Measurement" on the top page.)

The tool to measure is a unique measurement probe called a "coaxial resonator"(PATENT No.3691812). The measurement can be chosen at a five-point simultaneous measurement mode or single-frequency measurement mode.
Type1: 0.8/2.45/4.2/5.8/7.6GHz Type2: 1/3/5/7/9GHz
Type3: 2/6/10/14/18GHz

Choose the specific frequency from the "frequency setting" list.

The result of 5-points simultaneous measurement

The probe can handle materials of any shapes as long as there is one flat surface. The non-destructive measurement is
achieved by simply placing the material on the surface of the probe. It is suitable to measure for various solid-state samples such as plastics, ceramics, various resin, liquid crystal polymer, connector, glass, and others.
(*Please see the movie titled "3.Open Coaxial Probe" on the top page.)

If a sample material is placed on the probe, the evanescent electrical field leaks from the probe tip into the sample material. This electrical field changes with the dielectric properties of the material, which in turn changes the resonant frequency and the Q factor of the whole cavity. The dielectric properties (εr, tanδ) are then calculated from the changed resonance.
(*Please see the movie titled "3.Open Coaxial Probe" on the top page.)

The random error of the epsilon is estimated to be less than 1%, and the error of the tangent delta is less than 5%. The absolute accuracy will be confirmed by the reference materials. Two different materials are used as references. By calculating the relative difference between the measurement results of the references and a sample material, external error sources (eg.room temperature) are eliminated. Most important for accurate measurements is a firm contact between the sample material and the surface of the coaxial probe. Only a tiny gap might significantly change measurement results. Microwave Dielectrometer has a vacuum absorption attachment equipped on the probe tip. The sample contacts with the probe firmly and the stable and accurate measurement is possible.
(*Please see the movie titled "1.AET Microwave Dielectrometer" on the top page.)

Materials to be tested

The materials to be tested are required to have at least one flat and smooth surface (larger than 10mm × 10mm). The sample shape is arbitrary and the sample dimension should be larger than 10mm × 10mm × 0.5mm. To measure thin film materials, the film have to be stacked to get a total thickness greater than 0.5mm.

The evanescent field does not penetrate deep enough into high epsilon materials, which makes an accurate measurement of the dielectric constant difficult. For small loss tangent, the total loss of the probe is relatively higher than the conventional cavity resonator because of the leakage of the evanescent field. This is the main reason for the difficulty of measuring very small dielectric losses. We recommend the resonant cavity type microwave dielectrometer for the measurement of the sample with high epsilon and very small dielectric losses.

System Option

Microwave Dielectormeter uses the two different reference materials with well known dielectric properties. By calibrating the measurement parameters with these materials, this system achieves a quantitative accuracy. We use the two single crystals of SiO2 and MgO as the reference materials.

AET,Inc. set about the challenge of building a world wide sales network for the Microwave Dielectrometer. We are looking for local representatives who can promote and sell our system in North America, Europe, and Oceania.
If you have interest, contact us via Inquiry Form for more information.

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